The chemical conversion coating of aluminum and its alloys is known in the art as a process whereby the surface of the metal is chemically converted to a surface that more easily accepts applied coatings, i.e. paint, and for increases the corrosion resistance of the metal. An industry accepted process for the conversion coating of aluminum and its alloys makes use of known carcinogens such as chromates (see: MIL-DTL-80716B and/or ASTM B449). As a result, chromates and related toxic materials are being displaced by less toxic alternatives. Alternative conversion coatings in current use are based upon phosphates and/or anodizing or oxidation of the metal. Oxidized or phosphate generated conversion coatings tend to be brittle. In addition the processes require the use of long involved cleaning procedures involving toxic fluorides (see: Biestek, T., and Weber, J.: “Electrolytic and Chemical Conversion Coatings”, Portculis Press. Ltd., Queensway House, 2 Queensway, Redhill Surrey, RH1 1QS, 1976 and Wernick, S., Pinner. R. “The Surface Treatment and Finishing of Aluminum and its Alloys”, ASM International Metals Park, Ohio, 1987).
A typical A typical process for Aluminum and its alloys would involve: Hot alkaline soak cleaner at about 150 degrees F. for three to five minutes, D.I water rinse, dip in a strong acid solution to remove unwanted alloyed metals and/or metal oxides, rinse in D.I. water, conversion coating in a hexavalent chromium based solution and a final water rinse. Such a surface need to painted shortly after being produced as it will quickly form a hydrophobic surface and as a result will not easily accept applied coatings. Electroplating or non-electrolytic plating of aluminum and its alloys requires all of the above steps (with the exception of processing in a chromate conversion coating solution) and the application of an immersion zinc coating to provide for a uniform and even plating surface. These processes are rather difficult to properly apply and even with the use of the above processing steps, the plating of aluminum and its alloys is a very difficult process. (see: http://www.pfonline.com/articles/019601.html).